[llvm] [LoopInterchange] Forbid interchange when the dependency is confused (PR #78533)
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Wed Jan 17 17:51:58 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: None (ShivaChen)
<details>
<summary>Changes</summary>
https://github.com/llvm/llvm-project/issues/47259
A confused dependency(*f) in loop should prevent interchange in loops i and j.
void test_deps() {
for (int i = 0; i <= 3; i++)
for (int j = 0; j <= 3; j++) {
*f ^= 0x1000;
c[j][i] = *f;
}
}
---
Full diff: https://github.com/llvm/llvm-project/pull/78533.diff
6 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/LoopInterchange.cpp (+7)
- (modified) llvm/test/Transforms/LoopInterchange/lcssa.ll (+2-2)
- (modified) llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll (+1-1)
- (added) llvm/test/Transforms/LoopInterchange/pr47259.ll (+55)
- (modified) llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll (+3-3)
- (modified) llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll (+5-15)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 277f530ee25fc1..0ea8244924c0f3 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -123,6 +123,13 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
// Track Output, Flow, and Anti dependencies.
if (auto D = DI->depends(Src, Dst, true)) {
assert(D->isOrdered() && "Expected an output, flow or anti dep.");
+
+ if (D->isConfused()) {
+ LLVM_DEBUG(dbgs() << " Confused dependency between:\n"
+ << " " << *Src << "\n"
+ << " " << *Dst << "\n");
+ return false;
+ }
// If the direction vector is negative, normalize it to
// make it non-negative.
if (D->normalize(SE))
diff --git a/llvm/test/Transforms/LoopInterchange/lcssa.ll b/llvm/test/Transforms/LoopInterchange/lcssa.ll
index b41eba4ef56173..d3a0675caa7997 100644
--- a/llvm/test/Transforms/LoopInterchange/lcssa.ll
+++ b/llvm/test/Transforms/LoopInterchange/lcssa.ll
@@ -180,7 +180,7 @@ for.end16: ; preds = %for.exit
; REMARK: Interchanged
; REMARK-NEXT: lcssa_05
-define void @lcssa_05(ptr %ptr) {
+define void @lcssa_05(ptr noalias %ptr) {
entry:
br label %outer.header
@@ -225,7 +225,7 @@ for.end16: ; preds = %for.exit
; REMARK: UnsupportedExitPHI
; REMARK-NEXT: lcssa_06
-define void @lcssa_06(ptr %ptr, ptr %ptr1) {
+define void @lcssa_06(ptr %ptr, ptr noalias %ptr1) {
entry:
br label %outer.header
diff --git a/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll b/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
index def68ca3cd07eb..3b31c2634be71e 100644
--- a/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
+++ b/llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll
@@ -27,7 +27,7 @@
; REMARKS-NEXT: Name: Interchanged
; REMARKS-NEXT: Function: pr43326-triply-nested
-define void @pr43326-triply-nested(ptr %e, ptr %f) {
+define void @pr43326-triply-nested(ptr noalias %e, ptr %f) {
entry:
br label %for.outermost.header
diff --git a/llvm/test/Transforms/LoopInterchange/pr47259.ll b/llvm/test/Transforms/LoopInterchange/pr47259.ll
new file mode 100644
index 00000000000000..2a365a62795f81
--- /dev/null
+++ b/llvm/test/Transforms/LoopInterchange/pr47259.ll
@@ -0,0 +1,55 @@
+; REQUIRES: asserts
+; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -verify-dom-info -verify-loop-info \
+; RUN: -S -debug 2>&1 | FileCheck %s
+
+;; Test that a confused dependency in loop should prevent interchange in
+;; loops i and j.
+;;
+;; void test_deps() {
+;; for (int i = 0; i <= 3; i++)
+;; for (int j = 0; j <= 3; j++) {
+;; *f ^= 0x1000;
+;; c[j][i] = *f;
+;; }
+;; }
+
+
+; CHECK: Confused dependency between:
+; CHECK: store i32 %xor, ptr %arrayidx6, align 4
+; CHECK: %1 = load i32, ptr %0, align 4
+; CHECK-NOT: Loops interchanged.
+
+ at a = global i32 0, align 4
+ at f = global ptr @a, align 8
+ at c = global [4 x [4 x i32]] zeroinitializer, align 8
+
+define void @test_deps() {
+entry:
+ %0 = load ptr, ptr @f, align 8
+ br label %for.cond1.preheader
+
+; Loop:
+for.cond1.preheader: ; preds = %entry, %for.cond.cleanup3
+ %indvars.iv16 = phi i64 [ 0, %entry ], [ %indvars.iv.next17, %for.cond.cleanup3 ]
+ br label %for.body4
+
+for.cond.cleanup3: ; preds = %for.body4
+ %indvars.iv.next17 = add nuw nsw i64 %indvars.iv16, 1
+ %exitcond18 = icmp ne i64 %indvars.iv.next17, 4
+ br i1 %exitcond18, label %for.cond1.preheader, label %for.cond.cleanup
+
+for.body4: ; preds = %for.cond1.preheader, %for.body4
+ %indvars.iv = phi i64 [ 0, %for.cond1.preheader ], [ %indvars.iv.next, %for.body4 ]
+ %1 = load i32, ptr %0, align 4
+ %xor = xor i32 %1, 4096
+ store i32 %xor, ptr %0, align 4
+ %arrayidx6 = getelementptr inbounds [4 x [4 x i32]], ptr @c, i64 0, i64 %indvars.iv, i64 %indvars.iv16
+ store i32 %xor, ptr %arrayidx6, align 4
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %exitcond = icmp ne i64 %indvars.iv.next, 4
+ br i1 %exitcond, label %for.body4, label %for.cond.cleanup3
+
+; Exit blocks
+for.cond.cleanup: ; preds = %for.cond.cleanup3
+ ret void
+}
diff --git a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
index fa2021a15a0801..40cf1e9623b8c7 100644
--- a/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
+++ b/llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
@@ -156,7 +156,7 @@ for1.loopexit: ; preds = %for1.inc
; REMARKS-NEXT: Name: UnsupportedPHIOuter
; REMARKS-NEXT: Function: test4
-define i64 @test4(ptr %Arr, ptr %dst) {
+define i64 @test4(ptr %Arr, ptr noalias %dst) {
entry:
%gep.dst = getelementptr inbounds i64, ptr %dst, i64 42
br label %for1.header
@@ -234,7 +234,7 @@ for1.loopexit: ; preds = %for1.inc
; REMARKS-NEXT: Name: Interchanged
; REMARKS-NEXT: Function: test5
-define float @test5(ptr %Arr, ptr %Arr2) {
+define float @test5(ptr %Arr, ptr noalias %Arr2) {
entry:
br label %outer.header
@@ -274,7 +274,7 @@ for.exit: ; preds = %outer.inc
; REMARKS-NEXT: Name: UnsupportedPHIOuter
; REMARKS-NEXT: Function: test6
-define float @test6(ptr %Arr, ptr %Arr2) {
+define float @test6(ptr %Arr, ptr noalias %Arr2) {
entry:
br label %outer.header
diff --git a/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll b/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
index 03e3b4b7408b5c..b4f9d3f2a3685d 100644
--- a/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
+++ b/llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll
@@ -6,35 +6,25 @@
define void @test(ptr noalias %src, ptr %dst) {
; CHECK-LABEL: @test(
; CHECK-NEXT: entry:
-; CHECK-NEXT: br label [[INNER_PREHEADER:%.*]]
-; CHECK: outer.header.preheader:
; CHECK-NEXT: br label [[OUTER_HEADER:%.*]]
; CHECK: outer.header:
-; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OUTER_LATCH:%.*]] ], [ 0, [[OUTER_HEADER_PREHEADER:%.*]] ]
-; CHECK-NEXT: br label [[INNER_SPLIT1:%.*]]
-; CHECK: inner.preheader:
+; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OUTER_LATCH:%.*]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: br label [[INNER:%.*]]
; CHECK: inner:
-; CHECK-NEXT: [[J:%.*]] = phi i64 [ [[TMP0:%.*]], [[INNER_SPLIT:%.*]] ], [ 0, [[INNER_PREHEADER]] ]
-; CHECK-NEXT: br label [[OUTER_HEADER_PREHEADER]]
-; CHECK: inner.split1:
+; CHECK-NEXT: [[J:%.*]] = phi i64 [ 0, [[OUTER_HEADER]] ], [ [[J_NEXT:%.*]], [[INNER]] ]
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds [256 x float], ptr [[SRC:%.*]], <2 x i64> <i64 0, i64 1>, i64 [[J]]
; CHECK-NEXT: [[SRC_0:%.*]] = extractelement <2 x ptr> [[SRC_GEP]], i32 0
; CHECK-NEXT: [[LV_0:%.*]] = load float, ptr [[SRC_0]], align 4
; CHECK-NEXT: [[ADD_0:%.*]] = fadd float [[LV_0]], 1.000000e+00
; CHECK-NEXT: [[DST_GEP:%.*]] = getelementptr inbounds float, ptr [[DST:%.*]], i64 [[J]]
; CHECK-NEXT: store float [[ADD_0]], ptr [[DST_GEP]], align 4
-; CHECK-NEXT: [[J_NEXT:%.*]] = add nuw nsw i64 [[J]], 1
+; CHECK-NEXT: [[J_NEXT]] = add nuw nsw i64 [[J]], 1
; CHECK-NEXT: [[INNER_EXITCOND:%.*]] = icmp eq i64 [[J_NEXT]], 100
-; CHECK-NEXT: br label [[OUTER_LATCH]]
-; CHECK: inner.split:
-; CHECK-NEXT: [[TMP0]] = add nuw nsw i64 [[J]], 1
-; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[TMP0]], 100
-; CHECK-NEXT: br i1 [[TMP1]], label [[EXIT:%.*]], label [[INNER]]
+; CHECK-NEXT: br i1 [[INNER_EXITCOND]], label [[OUTER_LATCH]], label [[INNER]]
; CHECK: outer.latch:
; CHECK-NEXT: [[I_NEXT]] = add nuw nsw i32 [[I]], 1
; CHECK-NEXT: [[OUTER_EXITCOND:%.*]] = icmp eq i32 [[I_NEXT]], 100
-; CHECK-NEXT: br i1 [[OUTER_EXITCOND]], label [[INNER_SPLIT]], label [[OUTER_HEADER]]
+; CHECK-NEXT: br i1 [[OUTER_EXITCOND]], label [[EXIT:%.*]], label [[OUTER_HEADER]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
``````````
</details>
https://github.com/llvm/llvm-project/pull/78533
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